DESCRIPTION (Applicant's Abstract): It is proposed to study the structure and function of ribosomes using a range of biochemical approaches, including directed hydroxyl radical probing. These studies are focused on understanding the mechanism of action of the ribosome in protein synthesis. Specific plans are to study the rRNA environments of the ribosomal proteins, tRNAs, mRNA translational factors and the subunit interface at different stages of translation. A central question is whether elements of the rRNA move within the ribosome during different steps of the translational cycle. With the emergence of X-ray crystal structures for the 30S and 50S subunits, and the whole 70S ribosome, these studies are anticipated to progress even more rapidly than in recent years, and to begin to provide an understanding of the mechanism of at least some aspects of translation at the molecular, or even the atomic level.